Pulsed oscillator having oscillation terminating means independent of initiating pulse



March 7, 1961 R. A. FRYKLUND 2,974,293

PULSED OSCILLATOR HAVING OSCILLATION TERMINATING MEANS INDEPENDENT OFINITIATING PULSE Flled March 12, 1956 [N vew 7'01? I P066074 Way/a u/vov By A 7 ran/vs Y United States Patent Office PULSED OSCILLATOR HAVINGOSCILLATION TERMINATING MEANS INDEPENDENT OF INITIATING PULSE Robert A.Fryklund, Johnson City, N.Y., assignor to Raytheon Company, acorporation of Delaware Filed Mar. 12, 1956, Ser. No. 571,047

14 Claims. (Cl. 331-149) This invention relates to electronic switchingcircuits for the control of electrical energy and more particularly toan electronic switching or keying circuit wherein the passage of arelatively small current between a pair of spaced terminals or keyingcontacts may be utilized to control a relatively larger current for theenergization of oscillators, transducers, and the like. 7

In keying or switching systems ofthe type in which an energy orexcitation pulse'is provided for periodically controlling theconductivity of electron tubes or similar devices in response to theclosing of a pair of keying contacts, it has heretofore been diflicult,if not impossible, to provide a keying system which will permitconsistent keying over short pulse intervals foruse with pulse-producingdevices, such as short range depth sounders and the like, and at thesame time insure that the current passing the keying contacts is of asufiiciently small quantity that an arcing, which may occur when saidcontacts either open or close, is negligible. In addition, thedifiiculty involved in inserting a currentlimiting resistor in serieswith said keying contacts, or in shunting said contacts with a capacitorin an efiort to reduce arcing and erosion of the contacts, is morereadily understood when it is desired to key in a customary manner thegrid bias voltage of a conventional blocking oscillator, inwhich, inorder to initiate oscillation independently of the keying rate, it isnecessary that the keyed energy supplied to control said oscillator orassociated circuitry must be active for relatively short but accurateintervals of time. With this arrangement,

tacts, particularly under moist conditions, will tend to result in freerunning of the oscillator and production of pulses at a rate higher thanthe keying rate. The desirability of being able to provide accuratekeying control of a high amplitude pulse of fixed duration which isindependent of both the keying rate and the dwell time of the key andwhich imposes the least amount of erosion on the keying contacts,therefore, is readily appreciated.

I In accordance with the present invention, erosion due to arcing at thekeying contacts during the keying of a conventional electronicoscillator is overcome and other objects and advantages are obtained,first, by utilizing a gaseous discharge tube having a conventionallyhighimpedance grid-control circuit and by inserting the keying contactsin this circuit to control the discharge of a capacitor in the anodecircuit of said discharge tube to produce a pulse of fixed energycontent independently of the dwell time of the keying contacts, andthen, using this fixed energy pulse to initiate oscillation of theassociated electronic oscillator by momentarily overcoming the presetbias level of its bias control circuit. In addition, an energy storagedevice or capacitor is connected in the bias-control circuit for theoscillator, and is charged in response to such oscillation to change thebias level of the control circuit and terminate oscillationindependently of the duration of the initiating pulse. As a result, ahigh-amplitude pulse of fixed duration is produced by the keying circuitwhich avoids erosion of the keying contacts by limiting the flow ofcurrent therethrough and which, to an unexpected degree, is independentof the keying rate and of the dwell time of the key.

The foregoing and other objects of the invention will be best understoodfrom the following description of exemplifications thereof, referencebeing had to the accompanying drawing, wherein the single figure is acircuit diagram showing a keying system for a blocking oscillator and atransducer arranged in accordance with the invention. v I

Referring now to the accompanying drawing, the keying system of thisinvention is shown connected to,a crystal transducer 10 mounted betweenan electrode 11, which is connected to ground, and electrode 12, whichis connected in series with a conventional storage capacitor 13 to asource of oscillatory electrical energy in the output line 14 of ablocking oscillator 15. The upper electrode 12 of transducer 10 is alsoconnected through a capacitor 16 to a receiver (not shown) which'may beof a design customarily used with depth-sounding and ranging equipment.The blocking oscillator 15 is provided with a suitable oscillator tube17 having an anode 1 33, a grounded shield 19, a screen 20, and acontrol grid circuit consists of a grid leak resistor 28, a timingcapacitor 29, a shunting resistor 30, and a bias or discharge resistor31.

In the present embodiment of this invention, the value of timingcapacitor 29 and shunting resistor 30 is chosen to provide a freerunning pulse rate of several pulses per second in the absence 'of anadditional negative bias voltage introduced into the control circuitthrough resistor 32, rectifier 33, and bias terminal 34. The timingcapacitor 29 and shunting resistor 30, which control the free-runningpulse rate of the blocking oscillator, have values of .01 microfarad and13 megohms, respectively. The oscillator tube 17 is biased slightlybeyond cutofl? by an alternating current potential of 55 volts atterminal 34 and is rectified by a selenium rectifier 33, poled toprovide a negative potential with respect to ground across capacitor 35and bias voltage divider resistors 36 and 37. Thus, as noted, thenegative-bias voltage introduced through resistor 32 is of a valueslightly more than cutofi, and tube 17 will not oscillate until a sharppositive pulse is introduced to trigger or drive 2,974,293; PatentedMar. 7, 1961 v Thus, in accordance with the invention, a positive pulseis used to drive grid 21 momentarily less than cutoff to initiateoscillation. However, the oscillation so produced will not stop at thecompletion of the initiating pulse, but will continue until the chargeon timing capacitor 29, resulting from the flow of grid current duringconduction of tube 17, reaches a negative value substantially greaterthan that of the fixed .bias voltage from terminal 34. At this time,oscillation ceases in an abrupt manner, and the timing capacitor 29remains charged with this relatively high negative potential, which isthen dissipated by means of resistors 30 and 32 to a value equal to thefixed bias voltage, which is large enough to prevent oscillation. Inthis manner, the blocking oscillator is periodically energized toprovide an output pulse of fixed duration independently of the length oftime of an initiating pulse.

To provide an initiating pulse of fixed energy content for accuratetiming of the start of oscillation of tube 17, a thyratron or othergaseous discharge device 40 is provided, having an anode 41 connectedthrough a relatively large resistor 42 to a source of positive potentialof approximately 350 volts at terminal 26. This potential at the anode41 of tube 40 will charge the .01 microfarad capacitor 43 substantiallyto its full value during the period when the thyratron 40 is maintainednon-conductive by a negative potential being impressed upon controlelectrode 44 by means of bias resistors 45 and 46 and a negative sourceof voltage produced at the junction 39 of voltage divider resistors 36and 37. The discharge tube 40 may be a thyratron type 2D21 which has itsscreen 47 connected to bias resistor 45 through a suitable screenresistor 48. The cathode 49 of tube 40 is connected to the grid controlcircuit 38 at the side of timing capacitor 29 which is adjacent todischarge resistor 31. A negative bias potential of approximately --4 to-5 volts is provided at junction point 39 of the voltage dividerresistors 36 and 37, which is connected to ground through resistors 46and 53 and normally open switch or key 51. The thyratron tube 40 isinitially biased to a cutoff condition by the negative potential fromthe junction point 39 applied to control grid 44. However, when the key51 is depressed, this bias potential is removed, the grid 44 is returnedtoward ground potential through resistors 45 and 53, and tube 40 becomesconductive and discharges the charging capacitor 43. The discharge ofcapacitor 43 forces tube 40 to cutoff and produces a sharp pulse offixed energy content which, as noted, is introduced by means of cathode49 and resistor 31 into the control circuit 38 to drive the grid 21 ofoscillator tube 17 above cutoff and initiate oscillation in a mannerwhich is independent of the dwell time of key 51. In accordance with theinvention, the high resistance of the thyratron input circuit preventsthe handling of heavy currents by the key 51 and avoids harmful erosionof the keying contacts.

It should be understood that while the time constant of the thyratrondischarge circuit is not critical, it should be in the order of theperiod of the fastest keying rate. Accordingly, for typical echo-rangingapplications, the capacitance of the charging capacitor 43, as noted,may be approximately .01 microfarad, or sutficiently large to provide asharp positive voltage when discharged through the 1,000-ohm resistor 31to cutofi' tube 40, while the value of the anode resistor 42 isapproximately 2.0 megohms which, after cutoff of tube 40, will chargecapacitor 43 prior to a second closing of the key 51. It should benoted, however, that when the key 51 is closed there is a small currentsurge due to the discharge of the internal capacity of the keyingcircuit, particularly when long keying leads are used. In this instance,circuit capacity due to the keying leads, which may be represented by acapacitor 52, can be readily limited to an extremely low value by meansof a resistor 53 inserted in the keying lead and mounted as close to thekey as possible. This resistor 53 would normally be of a low resistancevalue of a 1,000 ohms or less in comparison to resistors 45, 46 and 48which, in this circuit application, are approximately 100,000 ohms.Moreover, resistor 53 can usually be omitted from the keying circuitwhen keying leads of average length are used. Thus, as noted, when key51 is depressed, a high amplitude pulse of fixed length is provided forthe transducer 10, independently of the keying rate and the dwell timeof the key.

In addition, it will be appreciated that many variations of the featuresshown and described herein in connection with a single embodiment of theinvention illustrated will occur to those who are skilled in the art towhich the invention relates. For example, the key 51 could be of themomentary-contact-type, actuated by a rotating cam disk whichperiodically closes the key against the action of a retaining springwhich tends to hold the key open. Furthermore, a source of directcurrent of suitable value could be connected to terminal 34 and theselenium rectifier 33 could be omitted. Furthermore, other types ofthyratron and oscillator tubes may be employed in connection withditferent values of circuit parameters. Accordingly, it is desired thatthis invention be not limited to the particular details of theembodiment disclosed herein, except as defined by the appended claims.

What is claimed is:

1. In combination, a keying system comprising an electronic oscillator,a gaseous discharge tube circuit including a gaseous discharge tube, asource of initiating voltage and electrical switching means in saiddischarge tube circuit for controlling the initiation of conduction ofsaid gaseous discharge tube, said discharge tube circuit including acapacitor coacting with said conduction of said discharge tube toproduce a pulse of fixed energy content independently of the continuedoperation of said electrical switching means, said electronic oscillatorhaving an input circuit responsive to said pulse of fixed energy contentto be triggered into oscillation for a predetermined period of timeindependently of the duration of said pulse, and an energy storagedevice responsive to said oscillation to inhibit said oscillationindependently of the time of termination of said pulse of fixed energycontent.

2. An oscillator keying circuit comprising an electronic oscillator, agaseous discharge tube having an input and output circuit including agaseous discharge tube, means in said discharge tube input circuitinitiating conduction of said gaseous discharge tube, said gaseousdischarge tube output circuit having a capacitor therein coacting withsaid conduction of said discharge tube to produce a pulse of fixedenergy content independently of the continued operation of said firstrecited means, said electronic oscillator having an input circuitresponsive to said pulse of fixed energy content to initiate oscillationfor a period independent of the duration of said pulse of fixed energycontent, and capacitive means connected in said input circuit toterminate said oscillation prior to initiation of the next succeedingpulse of fixed energy content.

3. An oscillator keying circuit comprising a gaseous discharge tube,capacitor means in circuit with said discharge tube for providing afirst relatively short pulse of fixed energy content, an electronicoscillator arranged to oscillate over a relatively long period of timecompared to said first pulse when triggered by said first pulse, meansto trigger said electronic oscillator in response to said first pulse,capacitor means responsive to said oscillation of said electronicoscillator to inhibit after a predetermined time said oscillationindependently of the termination of said first pulse, and means activein response to inhibition of said oscillation to restore said electronicoscillator to oscillation upon the production of the next succeedingenergy pulse.

4. In combination, an electrical switch provided with electricalcontacts, a gaseous discharge tube having an input circuit adapted torender said discharge tube conarr/gags ductive in response to a changein the state of the contacts of said electrical switch, said dischargetube having an output circuit for providing a pulse of fixed energycontent in response to conduction of said discharge tube, an electronicoscillator arranged to oscillate in response to said pulse of fixedenergy content, and an energy storage device responsive to saidoscillation to inhibit said oscillation independently of the time oftermination of said pulse of fixed energy content.

5. In combination, a normally free-running oscillator including anelectron tube having an anode, a cathode and a control grid, means forproducing a pulse of fixed energy content at predetermined timeintervals, means biasing said oscillator tube control grid to a firstnonconductive level with respect to said cathode, circuit meansresponsive to the production of said pulse of fixed energy content formomentarily biasing said oscillator control grid to a conductive level,thereby to initiate oscillation of said oscillator tube, capacitor meansresponsive to said oscillation to bias said control grid of saidoscillator tube to a second nonconductive level with respect to saidcathode independently of the time of termination of said energy pulse,said capacitor means coacting with said circuit means on termination ofsaid oscillation to change said bias from said second nonconductivelevel to said first nonconductive level prior to initiation of a secondpulse offixed energy content.

6. In combination, an electronic oscillator having a control circuitarranged to provide oscillation over a predetermined time interval, agaseous discharge tube having an input and an output circuit, saidoutput circuit having capacitance means for producing a pulse of fixedenergy content in response to conduction of said discharge tube, asource of voltage and switching means adapted to open and close for apredetermined time connected in said input circuit of said dischargetube for initiating said conduction .of said discharge tube upon closureof said switching means, said capacitance means controlling the durationof conductivity of said discharge tube independently of the time of theclosure time of said switching means, said electronic oscillator adaptedto be keyed into oscillation by said fixed energy pulse,. and an energystorage device responsive to said oscillation to inhibit saidoscillation independently of the time of termination of said pulse offixed energy content.

7. A keying circuit comprising an electrical switch having a pair ofinterruptable contacts adapted to open and close for a predeterminedtime, a gaseous discharge tube having a relatively high impedance inputcircuit as compared to a low impedance output circuit, said electricalswitch interposed in said input circuit for controlling the conductionof said discharge tube, said output circuit having a capacitance adaptedto provide a pulse of fixed energy content in response to saidconduction of said discharge tube, and an electronic oscillator havingan energy storage circuit adapted to permit oscillation in response tosaid fixed energy pulse for a predetermined length of time independentlyof the duration of said pulse, and an energy storage device responsiveto said oscillation to inhibit said oscillation independently of thetime of termination of said pulse of fixed energy content.

8. A keying circuit comprising an electrical switch having a pair ofinterruptable contacts adapted to open and close for a predeterminedtime, a gaseous discharge tube having an input circuit and an outputcircuit, said contacts of said electrical switch interposed in saidinput circuit for controlling the conduction of said discharge tube,said output circuit having a capacitance adapted to provide a pulse offixed energy content in response to said conduction of said dischargetube, and an electronic oscillator having a grid control circuitincluding a bias charging capacitor responsive to oscillation of saidelectronic oscillator to terminate oscillation independently of thedwell period of said interruptable contacts.

of said electrical switch and interposed in said input circuit forcontrolling the conduction of said discharge tube in response to theclosure of said contacts, said out put circuit having a capacitanceadapted to provide a pulse of fixed energy content in response toconduction of said discharge tube, and an electronic oscillator having abiased circuit adapted to initiate oscillation in response to said fixedenergy pulse for a predetermined length of time independently of theduration of said fixed energy pulse and independently of the closuretime of said interruptable contacts. V

10. In combination, an oscillator including an electron tube having ananode, a'cathode and'a control grid, a gaseous discharge tube having ananode, a cathode, and control electrode, means connecting said gaseousdischarge tube cathode in circuit with said electron tube control grid,switch means in the grid-to-cathode path of said discharge tube forrendering said discharge tube conductive, capacitor means in theanode-to-cathode path of said discharge tube for producing a pulse offixed energy content in response to said conductivity of said dischargetube, means normally biasing said electron tube grid to a firstnonconductive level with respect tosaid electron tube cathode, meansresponsive to the conductivity of said discharge tube for momentarilybiasing said electron tube to a conductive level to initiate oscillationtherein, energy storage means responsive to oscillation of said electrontube for biasing said electron tube grid to a second nonconductive levelwith respect to said electron tube cathode, and resistance meanscoacting with said energy storage mean-s to change said bias from saidsecond nonconductive level to said first nonconductive level prior toinitiation of the next succeeding energy pulse.

'11. An oscillator keying circuit comprising an electrical switch havinga pair of interruptable contacts adapted to open and close for apredetermined time, a gaseous discharge tube having an anode, cathodeand a control electrode, a source of voltage connected to said contactsof said switch and connected in circuit with said cathode and controlelectrode of said discharge tube,,a a capacitance in the anode circuitof said discharge tube,

for providing a discharge of fixed energy content independently of thedwell time of said interruptable contacts, a free-running oscillatoradapted to be triggered I into oscillation by said discharge for apredetermined period of time independently of the duration of saiddischarge.

12. An oscillator keying circuit comprising an electrical switch havinga pair of interruptable contacts adapted to open and close for apredetermined time, a gaseous discharge tube having an anode, a cathodeand a control electrode, said contacts of said switch connected incircuit with said cathode and said control electrode of said dischargetube, a capacitance in the anode circuit of said discharge tubeproviding a discharge of fixed energy content independently of the dwelltime of said interruptable contacts, an oscillator including an electron7 tube having a cathode, an anode and a control electrode,

said cathode of said discharge tube connected in circuit.

7 nonconductive level after termination of oscillation and prior toproduction of the next succeeding discharge.

13. An oscillator keying system comprising an electron tube having atleast a cathode, an anode and a control grid, at grid-to-cathode controlcircuit for said tube including a resistor and a capacitor, a source ofgrid bias potential maintaining said capacitor and said control grid ofsaid electron tube at a first nonconductive level with respect to saidcathode, keying circuit means to apply a pulse of fixed energy contentfor momentarily biasing said control grid to a conductive level, therebyto initiate oscillation, means responsive to conduction of said electrontube to charge said capacitor toa second nonconductive level withrespect to said cathode, and resistor means dissipating said charge onsaid capacitor to said first nonconductive level prior to initiation ofa second energy pulse.

14. An oscillator keying circuit comprising an electron tube having atleast a cathode, an anode and a control grid, at grid-to-cathode controlcircuit for said tube including a resistor and a capacitor, a source ofgrid bias potential maintaining said capacitor and said control grid ofsaid electron tube at a first nonconductive level with respect to saidcathode, a keying circuit comprising a pair of interruptable contacts,means responsive to said keying circuit to apply a pulse of fixed energycontent for momentarily biasing said control grid to a conductive level,thereby to initiate oscillation, means responsive to conduction of saidelectron tube to charge said capacitor to a second nonconductive levelwith respect to said cathode, and resistor means dissipating said chargeon said capacitor to said first nonconductive level prior to initiationof a second energy pulse, and resistive means in circuit with saidkeying means limiting current through said interruptable contacts.

References Cited in the file of this patent UNITED STATES PATENTS i-2win

